Method of and apparatus for forming venetian blind slats



A. B. WILSON Jan. 4, 1944.

METHOD OF AND APPARATUS FOR FORMING VENETIAN BLIND SLATS Filed July 26, 1940 2 Sheets-Sheet 1 HYVENTOR. Y flercfi mom A ATTORNEYS A. B. WILSON Jan. 4, 1944.

METHOD OF AND APPARATUS FOR FORMING VENETIAN BLIND SLATS Filed July 26, 1940 2 Sheets-Sheet 2 INVENTOR. fijenii 7&2607;

BY I M W I ATTORNEYS.

Q QR

r uwllvlilnJllil Patented Jan. 4, 1944 METHOD OF AND APPARATUS FOR FORM- ING VENETIAN BLIND SLATS Allen B. Wilson, Evanston, Ill., asslznor to Acme Steel iCompany, Chicago, 111., a corporation of Illino s Application July 26, 1940, Serial No. 347,593

19 Claims. (Cl. 153-54) This invention relates to improvements in methods of and apparatus for forming metallic Venetian blind slats and the present invention is a modification of, or an improvement upon. the invention described and claimed in my prior copending application Serial No. 239,229, filed November 7, 1938, now Patent No. 2,294,434, granted Sept. 1, 1942.

In said application, there is disclosed a method of making metallic Venetian blind slats by a two-stage process adapted to produce straight slats having parallel edges and a curved cross section which imparts to the slats the necessary stiffness. The manufacture of Venetian blind slats from strip steel or other strip metal is rendered difficult by the fact that ordinary commercial strip material is not perfectly flat, but is full of pockets and other irregularities, so that attempts to convert a commercial strip into a form having a curved cross section by any of the usual rolling and bending processes have produced products which are not straight and do not have parallel edges so that they are not suitable for the construction of Venetian blinds. The process disclosed in said application overcomes these'diiflculties by first stretching lonitudinally the intermediate portion of an elongated metal strip by a stress exceeding the elastic limit of the metal, the degree of tension exerted upon the metal being such that the irregularities in the portion subjected to the stretching operation are removed so that all parts of this intermediate portion would be under compression if the tensile stresses were removed. Having thus established a known condition in the metal strip, as distinguished from the uncertain and unknown condition in the commercial material as it exists at the beginning of the process, the elongated strip having its intermediate portion stretched is then bent transversely between'rolls and the strip is supported in advance of and following the rolls in such a manner that tensile stresses are set up in the strip between the points of support and the marginal portions thereof at the place of bending, thereby causing the lateral portions of the strip to'be stretched tdsubstan- V ficulties arise from the fact that successive portions of the commercial elongated metal strip which is employed, and different strips which are specified as being of the same gauge, are not. in fact, of precisely uniform gauges and this causes successive parts of the same strip, or,

more frequently, diflerent strips which are supposed to be of the same gauge, to assume diner ent degrees of transverse curvature after passing through the forming rolls which are employed in the second stage of the process for bending the strip transversely while the lateral edge portions thereof are being stretched longitudinally. The strip steel which is commonly employed in the manufacture of Venetian blind slats is relatively hard and thin and it has some resilience so that when .the completed slat is bent from its normal shape ,it tends to return immediately to its original condition. This material may vary substantially in gauge. For example, strip steel specified as 0.008 inch in thickness may vary from .00725 to .00875 inch,'and this may cause a variation of as much as .0015 inch in the thickness of the finished slats. Whatever the gauge, it is necessary in passing the strip through the forming rolls in the second stage of the process to bend the material transversely to a greater degree than that desired in the finished prbduct.

because of the tendency of the material to spring back from the condition to which it is in-.- itially bent. Thick material takes a. set more readily than thin material when bent and does not spring back to the same. degree, so the variation in gauge produces a variation in the transverse curvature of the finished product. The forming rolls may be selected to give the desired curvature for the thinnest material to be used but the heavier gauges will not have that curvature because the heavier gauges retain more of the' initial excess curvature imparted thereto by the rolls. In order to produce the same transverse curvature regardless of variations in gauge, it is therefore necessary to use a'difl'erent set of forming rolls for each gauge of commercial material used.

The principal object of the present invention is to improve upon the process described above by making it possible to use the same forming rolls on all strip material of the same commercial gauge within the limits of the usual variations in that gauge and with the result of producing a product having a uniform transverse curvature. It has been found that this may be accomplished by combining with the two-stage process of the former invention a third stage in which the transversely curved strip material, after passing through the forming rolls of the second stage,

. is flexed in a direction transverse to its line of travel, thereby buckling or progressively flattening the strip and thus temporarily removing from successive portions thereof most of the transverse curvature which has beenimparted thereto by the forming rolls. After passing through this flattening operation, the transverse curvature returns to the strip, due to its own resiliency, but to a lesser degree, and a greater degree of curvature is removed in this manner from the strip material which has thegreater thickness. The extent of permanent reduction of the transverse curvature effected by the progressive fiattening operation is proportional to the thickness of the material and since the thicker material naturally assumes a greater curvature in the forming rolls, the result is that all of the strip ing and progressive flattening of the strip as it emerges from the second stage of the process may preferably be accomplished by rolls which deflect the material from its normal path and cause it to form a loop. This loop may be utilized not only for flexing the material and removing irregularities in its transverse curvature but also to provide slack in the strip so that the strip may be arrested periodically, at a point following the place of flexing, by shearing knives which cut of! the strip in predetermined lengths suitable for Venetian blind slats. At each operation of the shearing blades, the travel of the strip will be arrested at the place where the shearing occurs and at each such interval the extent of the loop in the strip which is formed by the buckling or flexing operation will increase momentarily until the strip is again permitted to move longitudinally at the place of shearing. In this way, the shearing operation may be performed conveniently upon the moving strip without interrupting its travel through the forming rolls and without arresting the buckling operation. These and other objects of the invention will appear more fully hereinafter.

The nature of the invention will be understood from the following specification, taken with the accompanying drawings, in which one embodiment of the improved apparatus capable of carrying out the improved method of the present invention is illustrated. In the drawings Figure 1 shows a somewhat diagrammatic side elevation of one form of the improved apparatus which may be employed in straightening a metal the direction of the arrow I! by means of a series strip and stretching portions thereof between its longitudinal edges preliminary to imparting to the strip a continuous transverse curvature which is effected by other apparatus performing the second stage of the process;

Fig. 2 shows an enlarged vertical section through a portion of the apparatus illustrated in Fig. 1, illustrating the straightening and stretching rolls and portions of the adjacent friction rolls;

Fig. 3 shows an enlarged vertical section on the line 3-3 of Fig. 2, illustrating the roll by which the metal strip is stretched longitudinally between its longitudinal edges while being passed thereover under tension;

Fig. 4 is an enlarged vertical section taken on the line 4-4 of Fig. 2, illustrating one of the rolls for straightening the metal strip preliminary to stretching longitudinally the intermediate portion thereof;

Fig. 5 shows a top plan view, in somewhat diagrammatic form, of the complete apparatus which is employed in carrying out the second stage of the process by imparting to the strip a continuous transverse curvature, buckling the strip to remove irregularities in the degree of transverse curvature and" finally cutting off the strip;

Fig. 6 shows a side elevation-of the apparatus illustrated in Fig. 5;

Fig; '7 shows an enlarged vertical section taken on the line 1-1 of Fig. 6;

Fig. 8 is an illustrative transverse section of one part of the metal strip, taken on the line 8-8 of Fig. 6, showing the condition of the strip after it emerges from the forming rolls and before the degree of transverse curvature has been lessened and rendered uniform by subjecting the strip to the buckling operation; and

Fig. 9 .is an enlarged transverse section taken ,on the line 9-9 of Fig. 6, showing the condition of the, transverse curvature in the final product which forms a Venetian blind slat.

I It is desirable for reasons of economy to form Venetian blind slats from commercial strip steel or the like 'but this commercial material usually possesses not only the variations from a perfect flat condition which were referred to above but also it frequently possesses a lateral curvature in its own plane which is commonly known as camber. The apparatus of the present invention is therefore preferably constructed to eliminate this camber in the strip preliminary to stretching the intermediate portions of the strip in the first stage of the process. The method and apparatus for removing camber do not in themselves constitute a part of the present invention as they are described and claimed in the United States patent of Chester M. MacChesney No, 2,140,533, dated December 20, 1938, and in applicants copending application, Serial No. 246,024. As illustrated in Figs. 1 to 4, inclusive, of the drawings, the apparatus of the present invention is formed to receive and operate upon an elongated metal strip 15, of steel or the like, which is shown as being withdrawn from a reel l6 and moved in of driven friction rolls I8 which are .comparatively large in diameter and which are arranged in zigzag fashion so thatthe strip is compelled to follow an irregular path when passing through this series of rolls, thereby obtaining a large area of contact between the strip and the surface of each roll. The strip [5 then passes in zigzag fashion through a series'of parallel straightening rolls l9 which are comparatively small in diameter and which operate as idler rolls, being arranged with their axes in one plane so that as the strip passes over one roll and .beneath the next following roll it is bent back and forth and compelled to follow a sinuous path. Although the strip is preferably restrained against lateral movement as it passes through the rolls l9, as explained in the said patent of Chester M. MacChesney, it has been found, when operating upon hard strip metal of very fine gauges, which are preferably used in the manufacture of slats .for Venetian blinds, to permit some lateral movement of the strip whileit is being straightened. After passing through the rolls IS, the strip l5 then passes through a series of friction rolls 20 which are power driven and which pull the strip l5 under tension through the rolls I9. Upon emerging from the rolls 20, the strip l5 may pass directly to the apparatus which performs the succeeding steps of the process, and which is illustrated in Figs. 5 and 6, or the strip l5 may be wound upon a reel 2| which maintains the strip under. sufficient tension in the process of winding to hold it in contact with the friction rolls 20. The friction rolls 2|! are preferably 'spindle. The extremity of each spindle, outslightly larger in diameter'than the friction rolls I8 when the rolls of these two series are driven at the same angular speed, or the rolls 2!] are driven slightly faster than the rolls I8 so that the peripheral speeds of the rolls 2!] are greater than the peripheral speeds of the rolls I8, thereby creating a substantial tension in the strip I5.in a longitudinal direction as it passes through the intervening idler rolls I9. Some slippage is provided in the driving mechanism of the rolls so that the tension created in the strip I5 is not sufficient to elongate the strip generally throughout its width and the result is that, as the strip passes through the rolls I9, the, tension therein is suflicient to stretch the shorter edges of the strip until these shorter edges are of the same length as the opposite longer edged portions, thereby removing the camber. A brake is applied to the supply reel I6 to prevent the metal strip from being withdrawn therefrom too rapidly so that it is maintained in close contact with the rolls I8, and the driving mechanism which is connected to the-winding reel 2| is provided with a friction clutch which is adapted to slip when required so that ifthe reel 2| be driven at a greater speed than the friction rolls 29, as is the preferred practice, the friction clutch may slip and at the same time maintain the metal strip sufiiciently taut between the rolls and the reel 2| to bring about a tight winding of the strip in the coil while at the same time keeping the strip in close contact with the surfaces of the rolls 20.

The friction rolls I8 are mounted on shafts 23 which are preferably geared together so that they rotate in unison at the same speed and the friction rolls 2B are mounted on shafts 24 which are also preferably geared together so that they are driven in the proper direction at the same speed. Each series of shafts is power driven and the driving mechanism of the two series of shafts may be connected together by a belt or the like so that they will operate in unison, although the arrangement is preferably such that the rolls 29 are driven at a slightly greater speed than the rolls I8 and some slippage in the belt or other connecting mechanism is provided to take care of the difference in the driving speeds so that tension will at all times be maintained in the strip passing through the rolls, as disclosed in said patent of Chester M. MacChesney.

The straightening rolls I9 are carried by a frame member 25 which is in the form of a heavy angle bar secured upon a base 26 by means of studs 21. The frame 25 has an upwardly extending flange 25*, shown in Figs. 3 and 4, in which are secured the inner reduced ends 30 of a series of stationary spindles or axles 30 upon which the rolls I9 revolve. These spindles are provided adjacent their inner ends with integral surrounding collars 3i] which coact with the outer face of the frame member 25 and the inner threaded ends of the member 30 are engaged by nuts 3| by which the spindles are clamped securelyin position on the frame. Each roll I9, except the last roll of the series at the left as viewed in Fig. 2, is in the form of a cylindrical sleeve adapted to revolve about the body portion of one of the spindles 39. Bushings 32 are mounted in each of the rolls I9 to coact with the supporting spindle 30 and the outer reduced end of each spindle is threaded to receive a washer 33 and a nut 34 by which the roll is held against endwise movement on the wardly of the, threaded portion on which the nut 34 is mounted, has a smooth cylindrical surface to engage one of a series of apertures in a supporting frame member 35 which is provided with transversely extended threaded holes to receive a number of set screws 36 by which this frame member is clamped in position on the outer ends of the spindles to hold them against vibration and in their proper spaced relation. The spindles 30 are located with their axes in a single horizontal plane and the metal strip I5 is carried over one roll and under the next one throughout the series of rolls so that the strip is compelled to follow a sinuous path which results in stretching the shorter edge portions of .the strip, whereby the edges assume the same parallel relationship and the surface of the strip becomes substantially flat and free of any substantial irregularities. The rolls I9 which are of cylindrical form are of the same size and in alignment with each other but they may be replaced by rolls of different sizes when it is desired to operate upon metal strips of different widths.

The roll I9 which is nearest to the friction rolls 20, being the last roll of the series of rolls I9, is constructed and mounted in the same manner as the other rolls I9 except that its outer peripheral surface is transversely curved, as shown at I9 in Fig. 3, thus giving this roll an annular convex outer surface which is symmetrical on opposite sides of a transverse plane passing through its middle point, so that as the metal strip I5 passes over this roll, while under a longitudinal tensile stress exceeding the elastic limit of the metal, the portion of the strip between its lateral edges is stretched longitudinally to give it a greater length than the edge portions of the strip. The minor irregularities in the strip are thus removed and its condition is such that if the tension were removed all parts of the strip between its edge portions would be under compression. The strip in this form is in i a condition where the portions of the strip between its lateral edges are adapted to buckle out of the plane containing the edges of the strip due to their greater length. This strip material may be immediately subjected to the next stage of the process or it may be supplied in coils to Venetianblind manufacturers or others who may subject it to the succeeding stages of the process hereinafter described.

In the next stage of the process, the metal form in which all parts of the strip have been stretched longitudinally to substantially the same extent and in which it has a permanent transverse curvature with all of its longitudinal elements lying parallel to each other in straight lines. As heretofore indicated, in order to obtain the desired degree of transverse curvature in the finished product, it is necessary to-impart to the strip a greater transverse curvature than that desired while it is passing through the second stage of the process, and in a' final or out to a predetermined extent and is rendered uniform .in different strips of the same width having slightly different gauges, as mentioned above.

For the purpose of treating a metal strip'having its intermediate portions elongated, as heretofore described, in order to stretch its edge portions and impart a permanent transverse curvain the outer periphery of the upper roll is engaged by the convex peripheral portion of the lower roll 4| as the rolls rotate. 4| are mounted upon shafts 42 and 43, respectively, which are power driven so that they rotate in unison with the same peripheral speeds. The groove 40 in the roll 40 may be substantially semicircular in cross section and the outer surface 4| of the lower roll may have a corresponding curvature on a radius which is sufllciently smaller to accommodate the thickness of the metal strip which passes between the two rolls. As the strip |5passes through the rolls 40 and 4| it assumes the form shown in Fig. 7, a transverse curvature being imparted to the strip, and at the same time the lateral edge portions of the strip are stretched longitudinally by reason of the provision of means for supporting the strip immediately in advance of and immediately following the place of transverse bending. These suporting means comprise a guide roll 45 in advance of the rolls 40' and 4| which is carried by the angularly projecting arm of a bracket 46 secured upon the upper end of a rod 41 which is mounted for vertical adjustment in a stationarystandard 48. The rod 41 and the standard 48 have a splined connection as shown at 49 and the lower portion of the rod is threaded as shown at 41 for engagement by the threaded hub portion of an adjusting wheel 50 which revolves in a recess formed in the standard. By adjusting this wheel, the rod "and the bracket 46 may be adjusted vertically for the p p se of causing the guide roll 45 to vary the elevation of the strip in advance of and in proximity to the portions of the rolls 40 and 4| which coact with the strip.

The supporting means for the strip also comprises another guide roll 5| which is carried by a bracket 52 mounted on a horizontal rod 53 and adjustable laterally on that rod by means of a horizontal adjusting screw 54. Both the rod 53 and the adjusting screw 54 are mounted in upright supporting members 55, shown in Fig. 5, and the adjusting screw 54 has a hand wheel 55 secured on the end thereof for the purpose of enabling the operator to shift the guide roll 5| laterally of the strip |5.- A collar 51 is secured on the screw 54 adjacent the supporting member 55 against which the adjusting wheel 55'is located so that endwise movement of the adjusting screw is prevented ,during its rotation. The guide roll 5| occupies a position within the concave recess on the underside of the strip as this strip emerges from the rolls 40 and 4|.

By adjusting the supporting roll 45 vertically and by adjusting the roll 5| laterally the strip l5, which moves through the rolls in the direction of the arrow 50, shown in Fig. 6, may be caused to stretch longitudinally in its lateral edge portions and to emerge from the rolls 40 in a straight line with its lateral edges parallel to The rolls 40 and 9,888,878 third stagev the transverse curvature is flattenek.

each other and with a transverse curvature. By varying the elevation of the roll 45, the degree.

of stretching of the lateral edge portions of the strip may be varied as compared with the degree of stretch of the intermediate portions, in order to cause the strip to assume any desired lon itudinal shape. The stretching effected by the passage of the strip through the rolls 45, 4|l4| and 5| fmay be confined substantially to the lateral edge portions of the strip and the effect is to stretch the lateral portions of the strip longitudinally until all portions of the strip have been stretched longitudinally to the same extent that the intermediateportion of the strip, at the longitudinal center line, was stretched in the v first stage of the process.

- and the places where it is supported by the rolls and 5| may vary considerably from 'faeture of Venetian blinds, for example;

an exact straight line path of travel because of the tendency of the metal to spring back pa'rt way from any position to which it is bent and the consequent necessity of supporting it in a manner to bend it beyond-the desired ultimate position or form it is to have in the finished product. A series of metal strips may have varying transverse curvatures upon emerging from the rolls 45, 4|l4| and 5|, as heretofore explained, because of the variations in the initial gauges of the different strips when they are introduced into the first stage of the process, the strips of heavier gauge having a lesser'tendency to spring back from the excessive degree of curvature to which they are intentionally bent than the strips of lesser gauge. It is because of this variation in the degree of transverse curvature, caused by variations in gauge, that it has been found desirable to subject the strip to a third stage operation.

In this third stage, the metal strip is passed beneath a cylindrical idler roll 6| mounted on a shaft 62 and it is then flexed and looped upwardly, as shown at l5, about an intermediate idler roll 53 mounted on a shaft 54 which is joumaled in brackets 55 suspended from a lever 66 pivoted at 81 on a fixed member and having its other end pulled downwardly by a coil spring 68. After passing above and around the roll 63, the strip passes downwardly and extends in a forward direction again between a pair of rolls 59 and Ill which are mounted on shafts 1| and 12, respectively. The rolls '69 and 10 are so spaced that they flatten out the metal strip but one of them ha an annular layer 69' of rubber or the like mounted on its periphery so that the gauge of the metal is not affected. The rolls 6! and III are power driven so that they advance the strip in the direction of shearing blades I3 and I4 which are adapted to cut oil the strip to form appropriate lengths for use in the manu- I! de.. sired, the floatingroll 53 maybe eliminated as the loop l5 will ordinarily have'suflicient stability without any inside support.

As the metal strip approaches the roll 5|, it has a cross section of substantial curvature, such as that shown in Fig. 8, but, as before explained, this cross section may vary in different strips of cylindrical surface of the roll BI and it is restored to the form having a curved cross section only after passing through the rolls 69 and Ill. It then emerges in the form of a strip having a curved cross section but a cross section in the case of ,heavier gauges, of less transverse curvature, as shown in Fig. 9. Each time that the upper movable shearing blade M is brought into operation, the advance movement of the strip i is temporarily'arrested and, at these times, the extent of the loop l5 above the intermediate roll 63 will be increased and the spring 88 will elevate the intermediate roll 63 accordingly. -When the blade 14 is again elevated, the strip will advance and the loop will decrease in size with a corresponding lowering of the intermediate roll 63. It has been discovered that as a result of this operation the degree of transverse curvature in the strip is not only lessened but is rendered uniform in different strips and also throughout each strip in case there are slight diflerences in gauge at different points longitudinally of the same strip. It is thus possible to use the same forming rolls in the second stage of the process upon all strips of the same commercial gauge although there may be variations inthe actual gauges of diflerent strips.

In certain of the claims the condition of the metal strip at the end of the first stage of the process is defined by reference to the stresses existing therein, which is merely-one way of defining the elongation of a portion of the strip which is effected by that stage and, where the portion elongated is defined as the portion between the edges or as an intermediate portion, it is to be understood that these definitions are to be construed in the light of the practical results to be accomplished and that a process or apparatus is to be considered to be within the scope of such claims even though the elongation effected by the first stage of the process is not precisely coextensive with the width 'of the strip and even though slight portionsof the original irregularities may still remain in the strip,'as it has been found that satisfactory straight slats may be produced when substantial portions at the edges of the metal are not elongated in the first stage of the process and when slight original irregularities still remain therein. It will be understood that various modifications of the method and of the apparatus may be made without departing from the scope of the claims.

I claim:

- 1. The method of forming a metal strip having a predetermined longitudinal shape and a nonplanar cross section, which consists in stretching one longitudinal portion of. a fiat metal strip to a greater length than the remaining portions by subjecting said first mentioned portion to longitudinal tension of such magnitude that if the tension were released all parts of that portion would be under compression, then bending the strip transversely and longitudinally stretching the portions of the strip which are so bent to the extent required to produce said predetermined longitudinal shape, and then temporarily flattening the strip to cause it to assume a substantially uniform cross-sectional shape throughout its le th.

a predetermined longitudinal shape and a nonplanar cross section, which consists in stretchin 'one longitudinal portion of a flat metal strip to a greater length than the remaining portions by subjecting said first mentioned portion to longitudinal tension of such magnitude that if the 'tension, were released all parts of that portion would be under compression, then bending said strip transversely to impart thereto a non-planar cross section and stretchin longitudinally the parts which are so bent until all parts of the strip have been stretched longitudinally to substantially the same extent, and then, flexing the strip 1' transversely to reduce successive parts thereof 2. The method of forming a metal strip having 7 temporarily to a substantially fiat cross-sectional shape. 7

3. The method of forming a metal strip having a predetermined longitudinal shape and a curved cross section, which consists in stretching the intermediate portion of an elongated flat metal strip to a greater length than the remaining portions by subjecting said first mentioned portion to longitudinal tension of such magnitude that if the tension were released all parts of that portion would be under compression, then bending the strip transversely and stretching longitudinally the portions on opposite sides of its longitudinal center line while the strip has that cross section, and then bending and temporarily flattening the strip progressively transversely of said center line. t

4. The method of forming a metal strip having a curved cross section, which comprises the operations of stretching longitudina the intermediate portion of a thin elongated metal strip by subjecting said intermediate portion to longitudinal tension of such magnitude that if the tension were released all parts of the metal of said intermediate portion would be under compression, moving the strip longitudinally and progressively bending successive portions of said strip into a curved cross-sectional form while confining the successive portions of the strip to that curved form and supporting the strip immediately in advance of and immediately following the place of confinement to efiect the longitudinal stretching of the lateral edge portions of the strip, and then progressively looping the strip transversely of its longitudinal axis and temporarily flattening successive portions thereof while the motion of the strip continues.

5. The method of forming ametal strip having a non-planar cross section, which comprises the steps of bending transversely into a nonplanar cross-sectional form a metal strip which has its intermediate portion stretched longitudinally with respect to the remaining portions,"

stretching longitudinally the lateral edge portions of the metal strip while it is confined to said cross-sectional form, and then bending the strip transversely to effect the progressive and temporary removal of said non-planar cros section.

6. The method of forming a metal strip having a curved cross section, which comprises the steps of bending transversely into a curved cross-sectional form a metal strip which has its intermediate portion stretched longitudinally with respect to the remaining portions, stretching longitudinally the lateral edge portions of said strip while it is confined to said curved cross-sectional form, and then moving the strip endwise and progressively but temporarily bending successive portions thereof transversely.

7. The method or rendering substantially unielongated metal strip having a varying crosssectional form in successive parts thereof which consists in running the strip longitudinally and bending the strip endwise and progressively and temporarily producing a flat cross section.

8. The method of reducing and rendering substantially uniform the transverse curvature of an elongated metal strip having a varying transverse curvature in successive parts thereof which consists in bending the strip endwise and progressively and temporarily flexing to a substantially flat cross section successive parts of the strip.

9. The combination in apparatus for forming a metal strip having -a predetermined longitudinal shape and a non-planar cross section, of means elongated substantially flat metal strip between its edges, means for thereafter bending the strip transversely and effecting a stretching of the edge portions of the strip to substantially the same extent as said portion between said edges was previously stretched, and means for thereafter flexing the strip transversely and temporarily modifying its cross-sectional form.

10. The combination in apparatus for forming a straight metal strip having a curved cross section, of means for stretching longitudinally the intermediate portion of an elongated substantially flat metal strip, means for thereafter bend.- ing the strip transversely to impart a curved cross section thereto and effecting simultaneously a stretching of the edge portions of the strip to substantially the same extent as said intermediate portion was previously stretched, and then moving the strip endwise and progressively bending it transversely to effect a temporary flattening of successive portions of the strip.

11. The combination in apparatus for forming a metal slat having a curved cross section ,from a metal strip having its intermediate portion elongated with respect to its lateral edge portions, of rolls having complementary concave and convex surfaces for bending the strip transversely to impart a curved cross section thereto,

means cooperating with said rolls for causing the edge portions of said strip to be stretched longitudinally as the strip passes through said rolls,

. vex surfaces for bending the strip transversely to impart a curved cross section thereto, means cooperating with said rolls for causing the edge portions of said strip to be stretched longitudinally as the strip passes through said rolls, and a series of bending rolls adapted to flex the strip transversely and to eflect a temporary flattening of successive portions thereof as the strip moves therethrough.

13. The method of forming a metal strip having a predetermined longitudinal shape and a curved cross section, which consists in running the strip for stretching-longitudinally the metal of an the stripa curved cross section approximating the desired cross section, and then progressively looping the strip transversely of its longitudinal axis and thereby temporarily removing the curved cross section in successive portions of the strip' while its motion continues to cause the strip to assume the desired curved cross section beyond the place where the looping occurs.

14. The combination in apparatus for forming a metal strip having alcurved cross section, of means for imparting to'a metal strip a nonplanar cross section and a predetermined "longitudinal shape, and means for progressively loop-- ing successive portions of the strip through an arc of such magnitude as to temporarily flatten successive portions of the strip. I

15. The combination in apparatus for forming a metal strip having a curved cross section, of means for moving an elongated metal strip endwise and imparting thereto a curved cross section and a predetermined longitudinal shape, and a pair of rolls between which said strip passes and which are relatively located to compel a progressive bending and temporary flattening of the moving strip.

16. The combination in apparatus for forming a metal strip having a curved cross section, of means for moving an elongated metal strip endwise and imparting thereto a curved cross section and a predetermined longitudinal shape, a roll about which said strip having a curved cross section is adapted to be bent transversely to form a loop, and two rolls arranged to coact with said strip to maintain said loop.

17. The combination in apparatus for forming a metal strip having a curved cross section, of means for moving an elongated metal strip endwise and imparting thereto a curved cross section and a predetermined longitudinal shape, a roll about which said strip having a curved cross section is adapted to be bent transversely to form aloop, two rolls arranged'to coact with said strip to maintain said loop, and a power driven roll having an annular surface portion engaging said strip opposite one of said last-mentioned rolls to feed the strip, i

18. The method of forming a metal strip having a non-planar cross section,,which comprises the steps of bending transversely into a non-planar strip. endwise and imparting tosuccessive portions of cross-sectional form a strip which has one longitudinal portion thereof stretched longitudinally with respect to the remaining longitudinal portions which are displaced laterally therefrom, stretching longitudinally the said laterallydisplaced portions of said strip while it is confined to said nonplanar cross section to which it has been bent, and then moving the strip endwise and progressively but temporarily bending successive portions transversely to the general direction of travel of the strip.

19. The combination in apparatus for forming a metal strip having a curved transverse cross section, of means for imparting to a long metal strip a curvedtransverse cross section and a predetermined longitudinal shape, and a pair of members having parallel elements between which said strip is then moved endwise and which are relatively located to compela progressive and temporary transverse flattening of the moving ALLEN B. WILSON. 

